This invention relates to a friction false-twisting device for imparting twists in a yarn running at a high speed.
Many kinds of friction false-twisting devices have been well known. One such false-twisting device comprises three shafts disposed at vertexes of a triangle, respectively, so as to be parallel to each other, and a plurality of friction discs having a yarn contacting surface disposed on the shafts and being supported for sequential positioning. These friction discs lie on a screw-thread and are partially juxtaposed. Such a false-twisting device can not only speed up the texturing speed, but can also facilitate easy threading up operations. Such a device, therefore, is suitable for use in carrying out two false-twisting methods. One of these methods is a draw-false-twist texturing method which comprises a step for drawing undrawn yarn or partially oriented yarn and a step for false-twist texturing the yarn simultaneously with or sequentially to the drawing step. The other method is a spin-draw-false-twist texturing method comprising a step for melt spinning a thermoplastic synthetic yarn and a step for carrying out the above-mentioned draw-false-twist texturing method.
However, when the above-mentioned conventional friction false-twisting device is utilized for false-twist texturing a yarn running at a speed above 400 m/min, defects such as abrasions of the friction discs created by frictional contact with the textured yarn occur. This defect is caused by the material of the contacting surface of the friction disc. That is, since the contacting surface of the conventional false-twisting device is usually made of polyurethane rubber, the durability of the friction disc is low.
A friction false-twisting device having discs with a ceramic coating thereon is also known. However, when the above-mentioned friction false-twisting device is utilized for false-twisting a yarn running at a speed above 400 m/min, although the durability of the friction disc is high enough, the friction disc can not impart sufficient twists to the yarn. As a result, the defect that the yarn quality of the textured yarn is low occurs.
The inventors of the present invention investigated the above-mentioned defects and found that in the conventional friction false-twisting device, having ceramic coated yarn contacting surfaces, the friction disc used does not have a suitable surface roughness and shape for false-twisting a yarn. In addition, it was found that the thickness of the conventional friction disc is too small for false-twisting yarns well. In this regard the inventors found that, when a yarn is friction false-twisted, the shape of the friction disc and the surface condition of the yarn contacting surface of the friction disc are important factors influencing the false-twisting of the yarn. In addition, it was also found that the yarn running angle between the yarn and the rotational axis of the friction disc, which is determined by the arrangement of the friction discs, is an important factor influencing the false-twisting of the yarn.
An object of the present invention is to provide a friction false-twisting device provided with friction discs having high durability.
Another object of the present invention is to provide a friction false-twisting device which can produce a fully and uniformly false-twisted yarn at a high speed above 400 m/min, even at a speed of more than 600 m/min.
A further object of the present invention is to provide a friction false-twisting device provided with discs having a specially designed shape and a specially finished yarn contacting surface.
Other objects of the present invention will be apparent from the following descriptions with reference to the accompanying drawings.
These objects are achieved by a friction false-twisting device comprising three shafts disposed at vertexes of a triangle so as to be parallel to each other and rotatable in the same direction, and a plurality of friction discs having a yarn contacting surface made of ceramic disposed on said shafts, said friction discs being positioned along a screw-thread and being partially juxtaposed, wherein said friction disc comprises, in a combination:
a pair of end surfaces disposed in parallel having a distance T (mm) between said end surfaces in a range between 5 and 8 mm; PA1 a curved surface disposed at a position between said end surfaces having a radius of curvature R (mm) in a range between 5 and 8 mm; PA1 a pair of connecting surfaces disposed at positions between said end surface and said curved surface having a smaller radius curvature r (mm) in a range between 1/6 R and 1/2 R, and; PA1 a yarn contacting surface comprising said curved surface and a pair of said connecting surfaces having a surface roughness of in a range between 1.sup.s and 6.sup.s.